1. Field of the Invention
The present invention relates to a stacked mounting structure, and particularly to a three-dimensional stacked mounting structure which is made by stacking a plurality of members in a directions of thickness of the members.
2. Description of the Related Art
For a structure which includes substrates on which electronic components are mounted, various structures have been hitherto proposed (refer to Japanese Patent Application Kokoku (Post Exam Application) No. Hei 4-38417 and Japanese Patent Application Laid-open Publication No. Hei 11-111914 for example). In Japanese Patent Application Kokoku (Post Exam Application) No. Hei 4-38417, a mounting structure related to an imaging unit which is provided at a front end portion of an endoscope 10 as shown in FIG. 15, is disclosed. Here, a technology of stacking a mount substrate in parallel with an imaging device 11 is described. In this technology, first of all, a mount board 12 is disposed in parallel with the imaging device 11. Next, the mount board 12 on which the imaging device 11 is mounted, and a mount board 13 on which components other than the imaging device 11 are mounted, are mounted via a spacer. Accordingly, it is possible to dispose the components mounted on the mount boards, in a space equivalent to a height of the spacer, which is developed. Consequently, it is possible to improve a packaging density of the stacked mounting structure. As a result, it is possible to reduce a size of the imaging unit which is provided at the front end of the endoscope.
Moreover, in Japanese Patent Application Laid-open Publication No. Hei 11-111914, a structure of a stacked mounting structure 20 which includes a memory module substrate 24, as shown in FIG. 16 is disclosed. An inner side of a substrate 21 which is facing is hollow. A plurality of electrodes is provided on both sides of the substrate 21. Moreover, the electrodes on a front surface of the substrate 21 and the electrodes on a rear surface of the substrate 21, which is facing, are connected electrically. At a portion connecting the electrodes, an anisotropic electroconductive film 22 is adhered to both sides of an electroconductive spacer 25. Thus, in Japanese Patent Application Laid-open Publication No. Hei 11-111914, a structure of the substrate 21 on which an electronic component 23 is mounted, is disclosed. In this structure, for joining the electroconductive spacer 25 and the anisotropic electroconductive film 22, an electrode is provided in a (on a) through hole which is provided in the electroconductive spacer 25.
In the structure disclosed in Japanese Patent Application Kokoku (Post Exam Application) No. Hei 4-38417, an electric conduction between the substrates which are disposed by stacking, is ensured by a lead wire 14. An automation of a job of joining the substrates by the lead wire 14 is difficult. For example, a job of disposing and soldering short lead wires on a minute structure which is disposed three-dimensionally, is impossible to deal with in an automatic packaging machine.
Therefore, the job of installing the lead wire 14 is to be carried out manually. Moreover, even with the job carried out manually, such mounting is categorized to be having a high degree of difficulty. A technology in which the automation is difficult, and the degree of difficulty of the job is high, leads to an increase in a mounting cost and a decline in productivity. Moreover, taking into consideration a size of the lead wire which can be handled in a manual job and a gap between the lead wires which can be controlled during the handling, a structure according to the conventional technology is not favorable for reducing a size of the mounting structure.
Moreover, in the structure disclosed in Japanese Patent Application Laid-open Publication No. Hei 11-111914, as it is evident in FIG. 16, an electrode having an area more than an outer diameter of the through hole is required to be provided on the electroconductive spacer 25. Therefore, it is difficult to narrow a pitch of a joining portion. In other words, it is difficult to reduce a projected area when the structure is viewed from a top. Furthermore, in this structure, the anisotropic electroconductive film 22 is used as a material for joining the electroconductive spacer 25 and the substrate 21. Therefore, there is a drawback that a resistance of the connecting portion between the electroconductive spacer 25 and the substrate 21 becomes high.
Thus, in the conventional mounting structure, it is difficult to ensure a favorable productivity for stacking a substrate via the spacer in order to ensure a mounting space of the electronic components. Moreover, it is also difficult to reduce the size such that a projected area in a direction of a plane of the substrate is decreased.